Jilin Zheng

Frequency tunable optoelectronic oscillator based on a directly modulated DFB semiconductor laser under optical injection.

A frequency tunable optoelectronic oscillator based on a directly modulated distributed-feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Through optical injection, the relaxation oscillation frequency of the DFB laser is enhanced and its high modulation efficiency can enable the loop oscillation with a RF threshold gain of less than 20 dB. The DFB laser is a commercial semiconductor laser with a package of 10 GHz, and its packaging limitation can be overcome by optical injection. In our scheme, neither a high-speed external modulator nor an electrical bandpass filter is required, making the system simple and low-cost. Microwave signals with a frequency tuning range from 5.98 to 15.22 GHz are generated by adjusting the injection ratio and frequency detuning between the master and slave lasers. The phase noise of the generated 9.75 GHz microwave signal is measured to be -104.8 dBc/Hz @ 10 kHz frequency offset.

Study on DFB semiconductor laser array integrated with grating reflector based on reconstruction-equivalent-chirp technique

A 4-channel distributed feedback (DFB) semiconductor laser array with incorporation of a grating reflector utilizing reconstruction-equivalent-chirp technique is theoretically studied and experimentally demonstrated. By integrating with a grating reflector, 40% increase of slope efficiency, about 10mA decrease of threshold current and 7dB increase of side mode suppression ratio (SMSR) are achieved with a deviation of wavelength spacing being less than 0.07nm. The SMSRs of all the lasers are higher than 60dB.

Study on Two-Section DFB Lasers and Laser Arrays Based on the Reconstruction Equivalent Chirp Technique and Their Application in Radio-Over-Fiber Systems

Two-section distributed feedback (TS-DFB) semiconductor lasers based on the reconstruction equivalent chirp technique is proposed. A four-channel TS-DFB laser array (TS-DFB-LA) is theoretically studied and experimentally demonstrated. Compared with the conventional one-section DFB lasers, the proposed TS-DFB lasers have much higher output efficiency and higher side-mode suppression ratio (SMSR) when both the facets of the laser cavity are coated with antireflection coatings. About 39% increase in output efficiency, more than 10 mA decrease in threshold current, and about 5 dB increase in SMSR have been achieved experimentally. Furthermore, experimental results show that the wavelength spacing accuracy of the four-channel TS-DFB-LA can be improved by tuning the injection current of one of the two sections. Using the two-section structure, the dynamic characteristics including small-signal frequency response, relative intensity noise, and spurious-free dynamic range are also improved significantly. A radio-over-fiber link utilizing the TS-DFB laser as directly modulated light source was experimentally achieved. About 50 MSymbol/s 64-QAM signal with 10 GHz carrier was transmitted from the TS-DFB laser. After 40 km transmission in single-mode fiber, the average error vector magnitude of the whole link is 2.97%.

Fabry-Pérot cavity based on chirped sampled fiber Bragg gratings.

A novel kind of Fabry-Pérot (FP) structure based on chirped sampled fiber Bragg grating (CSFBG) is proposed and demonstrated. In this structure, the regular chirped FBG (CFBG) that functions as reflecting mirror in the FP cavity is replaced by CSFBG, which is realized by chirping the sampling periods of a sampled FBG having uniform local grating period. The realization of such CSFBG-FPs having diverse properties just needs a single uniform pitch phase mask and sub-micrometer precision moving stage. Compared with the conventional CFBG-FP, it becomes more flexible to design CSFBG-FPs of diverse functions, and the fabrication process gets simpler. As a demonstration, based on the same experimental facilities, FPs with uniform FSR (~73 pm) and chirped FSR (varying from 28 pm to 405 pm) are fabricated respectively, which shows good agreement with simulation results.

Experimental demonstration of a fast tunable laser based on DFB semiconductor laser array using reconstruction-equivalent-chirp (REC) technique

We propose a novel approach of fast tunable laser, which uses high-speed driving circuit and DFB semiconductor laser array to achieve the fast switching of wavelength. We use single chip microcomputer and FPGA to form the control system, and a high-speed driving circuit to ensure the switching speed. The 8-channel DFB laser array was fabricated based on reconstruction-equivalent-chirp (REC) technique. The experimental result shows that the switching time of the wavelength is about 30 ns.

High efficiency and SMSR distributed feedback laser array integrated with passive grating reflector based on reconstruction-equivalent-chirp technique

We reported a 4-channel DFB laser array integrated with passive-grating-reflector utilizing reconstruction-equivalent-chirp technique. 53.3% increase of slope efficiency, 27.3% decrease of threshold current are obtained with >60dB SMSR and wavelength spacing deviation <; 0.07nm.

DFB Semiconductor Laser With Discrete Coupling Coefficient Based on the Equivalent Technique

An equivalently discrete coupling coefficient (EDCC) distributed feedback (DFB) semiconductor laser with EDCC grating is numerically investigated and experimentally demonstrated; the EDCC grating structure is designed by discretizing the duty cycle of sampled Bragg grating along the laser cavity, i.e., the cavity is divided into some subsections, and the duty cycle is constant in each subsection while it is different between two adjacent subsections, instead of the truly discrete coupling coefficient grating profile realized by discontinuously varying the duty cycle and/or etching depth of the uniform gating pitch. Moreover, the EDCC grating is fabricated by combining the conventional holographic exposure with a micrometer-level photolithography, which will simplify the fabrication process and reduce the fabrication cost. Based on experimental data, the analysis of spectral behavior as a function of injection current shows that the stable single-longitudinal-mode operation has been realized, even at large injection current and high temperature.

Monolithically Integrated Four-Channel DFB Semiconductor Laser Array With an Equivalent-Distributed Coupling Coefficient

An equivalent-distributed coupling coefficient (EDCC) distributed feedback (DFB) semiconductor laser is proposed, and a four-channel EDCC DFB laser array is experimentally demonstrated. In this paper, the EDCC grating profile is realized by varying the duty cycle of a certain subsection of the whole sampled Bragg grating (SBG) along the laser cavity, instead of the true DCC structure obtained by changing the height of the uniform grating pitch. Moreover, the EDCC grating array can be designed by stepping the sampling period of the SBG and fabricated by combining the conventional holographic exposure with a micrometer-level photolithography on the same wafer. The experimental results show that the uniform channel spacing in the array has been obtained and that the residual of the lasing wavelengths after linear fitting changes in the scope of -0.078 and 0.048 nm. Each laser has good single longitudinal mode operation with the minimum side-mode suppression ratio (SMSR) of about 47.65 dB and the average SMSR of 49.83 dB under the same injection current of 80 mA.

Experimental Demonstration of a Multicorrugation-Pitch-Modulated (MCPM) DFB Semiconductor Laser Based on Reconstruction-Equivalent-Chirp Technology

A multicorrugation-pitch-modulated (MCPM) distributed-feedback semiconductor laser is experimentally demonstrated for the first time to achieve stable single longitudinal mode (SLM) performance. The MCPM structure was equivalently realized based on a sampled grating using reconstruction equivalent chirp (REC) technology. The proposed REC-MCPM structure can effectively flatten the optical intensity distribution along the laser cavity, leading to the strong suppression in spatial hole burning. In addition, the REC-MCPM grating structures can be readily fabricated using conventional holographic lithography combined with low-cost standard micrometer-level photolithography. A proof-of-principle study both in a simulation and an experiment is presented in this paper. The fabricated 400-

再構成等価チャープ(REC)法を用いたDFB半導体レーザアレイに基づく高速可変同調形レーザの実験的実証【Powered by NICT】

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